1. Field of the Invention
This invention relates to a fluidized bed system having a spray nozzle therewithin. One such system is a Wurster system type of fluidized bed processor including an outer cylindrical partition disposed within the product container and a spray nozzle within the partition. The spray nozzle itself is shielded, preferably by being surrounded by a cylindrical partition extending from the orifice plate or screen at the bottom end of the product container to shield the spray nozzle tip.
2. Description of Related Art
Various different forms of spray coaters heretofore have been provided including the Wurster system type. These previously known devices may experience turbulent air flow immediately above the spray nozzle. Particles to be coated within the system may enter the liquid discharge spray pattern before the spray pattern has fully developed. This results in uncontrolled droplet formation upon those particles that enter the spray pattern too soon and effects the effectiveness of the system resulting in excessive agglomeration and relatively extensive processing time.
U.S. Pat. No. 3,110,626 to G. L. Larson et al. discloses an apparatus whereby coating discrete solids suspended in a moving air stream is carried out within the interior region of a velocity concentration control element mounted in the base region of a funnel-shaped coating chamber. However, such apparatus does not include any means for shielding the base of the spray pattern with an upwardly flowing column of air in order that the spray pattern may substantially develop before entrance thereinto of discrete solids to be coated.
U.S. Pat. No. 4,335,676 to Christian Debayeux et al. discloses a spouted bed granulating and/or coating apparatus wherein flow directing structure is provided to direct the gaseous flow stream in the upward direction for preventing contact and agglomeration of particles in the vicinity of the walls of the device. This patent fails to disclose structure by which the lower portion of the spray pattern is protected by an upwardly flowing column of air in order that the spray pattern may more fully develop before the entrance thereinto of particles to be coated.
U.S. Pat. No. 4,701,353 to Stanislaus M. P. Mutsers et al. discloses an apparatus whereby the liquid spray material is discharged out of a central channel as a vertically closed, conical film with a thrust exceeding the thrust of the gas stream for the purpose of causing the conical film to be nebulized to very fine droplets with the aid of the surrounding gas stream. The resultant spray pattern is not protected about its initial base end by an upwardly moving column of air disposed thereabout.
U.S. Pat. No. 4,960,224 to Gustav A. Magg et al. discloses an atomizing nozzle constructed in a manner to eliminate the need to provide a metering pump or flow meter for each atomizing nozzle of an associated fluidized coating bed with the control of the flow through each atomizing nozzle being accomplished by varying the internal bore size of the flow control tubes. However, this patent fails to disclose structure for shielding the resultant spray pattern from immediate entrance thereinto of particles to be coated before the spray pattern is reasonably developed.
U.S. Pat. No. 4,858,552 to Werner Glatt et al. discloses an apparatus whereby a fluidized current carries particles, while still plastic, upwardly through a channeling device for agglomerated material disposed at a distance above the perforated base causing the particles to impinge on the underside of a rotatable means providing for shaping the agglomerated material. The Glatt et al. apparatus does not disclose structure by which the particles to be coated are shielded against entry into the initially forming spray pattern.
U.S. Pat. No. 3,196,827 to D. E. Wurster et al. discloses a tubular partition defining an upbed therein into which an air and spray discharge pattern is directed and wherein a downbed of particles in near weightless suspension is disposed outwardly of the tubular partition, the spray nozzle being disposed below the bottom of the partition and above the associated air distribution plate or screen. With this device, particles being coated are also free to immediately enter the lower beginning portion of the spray pattern.